One of the biggest problems caused from vehicles using fossil fuel, such as gasoline and diesel oil, is creation of air pollution. A technology of using a secondary battery, which can be charged and discharged, as a power source for vehicles has attracted considerable attention as one method of solving the above-mentioned problem. As a result, electric vehicles (EV), which are operated using only a battery, and hybrid electric vehicles (HEV), which jointly use a battery and a conventional engine, have been developed. Some of the electric vehicles and the hybrid electric vehicles are now being commercially used. A nickel-metal hydride (Ni-MH) secondary battery has been mainly used as the power source for the electric vehicles (EV) and the hybrid electric vehicles (HEV). In recent years, however, the use of a lithium-ion secondary battery has been attempted.
High output and large capacity are needed for such a secondary battery to be used as the power source for the electric vehicles (EV) and the hybrid electric vehicles (HEV). For this reason, a plurality of small-sized secondary batteries (unit cells) are connected in series or in parallel with each other so as to construct a battery module, and a plurality of battery modules are connected in parallel or in series with each other so as to construct a battery pack.
In such a high-output, large-capacity secondary battery, however, a large amount of heat is generated from the unit cells during the charge and the discharge of the unit cells. When the heat generated from the unit cells during the charge and the discharge of the unit cells is not effectively removed, heat is accumulated in the unit cells with the result that the unit cells are degraded. Consequently, it is necessary to provide a cooling system for vehicle battery packs, which are high-output, large-capacity secondary batteries.
Generally, a cooling system for vehicle battery packs is constructed in an air-cooling structure using air as a coolant. In the air-cooling structure, air outside or inside the vehicle is introduced to cool the battery pack, and is then discharged out of the vehicle. For example, the cooling system may be constructed in a structure in which an air inlet part, through which air is introduced from a specific region outside or inside the vehicle, and an air outlet part, through which the air having passed through the battery pack, which has been heated, is discharged out of the vehicle, are mounted at a housing (a case), which surrounds the outer surface of the battery pack, and air is circulated by the driving force of a cooling fan such that the battery pack can be cooled by the circulated air.
In the case that air outside the vehicle is used as air for cooling the battery pack, it is necessary to control the temperature and the humidity of the air. Consequently, it is preferable to use air inside the vehicle, the temperature and the humidity of which are controlled at a specific level.
The air inside the vehicle, as well as the air outside the vehicle, contains fine dust, although there is a little difference between them. Such dust may cause a serious problem especially in a fuel cell, which uses air as one of material components for battery operation. For this reason, U.S. Unexamined Patent Publication No. 2005-8912 and Japanese Unexamined Patent Publication No. 2004-273311 disclose technologies for effectively removing dust by means of a filter mounted at an air supply unit of a fuel cell.
As previously described, air is used to cool the secondary battery pack. Consequently, seriousness of problems due to dust in the case of the battery pack is lower than that in the case of the fuel cell. However, when such fine dust is introduced into the battery pack along with the air, and, as a result, the dust is excessively accumulated on unit cells of the battery pack, the cooling efficiency is decreased. Furthermore, when metal dust component among the fine dust is accumulated on an electrical connecting part and a circuit board of the battery pack, the malfunction or short circuits of the battery pack may be caused.
Consequently, Korean Registered Patent No. 494936 discloses a technology for removing dust by means of a filter mounted at an air inlet part of the battery pack, and Korean Registered Patent No. 202509 discloses a technology for removing dust and moisture by means of a filter mounted at the rear of a cooling fan of the battery pack.
The above-mentioned patents disclose the provision of the filter for removing the dust. However, the detailed construction of the filter is not disclosed in the patents. It can be understood from the review of the patent specifications that a single filter is mounted to remove dust. In this case, various-sized dust is filtered by the single filter with the result that the filter replacing cycle is very short. Also, an expensive filter is needed to filter fine dust. Especially, it is difficult to remove metal dust, which may cause the malfunction or short circuits of the battery pack.
Meanwhile, the vehicle battery pack must be mounted in a restricted space in the vehicle, and therefore, it is preferable that the vehicle battery pack be constructed in a compact structure. The size of the vehicle battery pack is decided depending upon the size of the battery module, which is constructed by stacking unit cells one on another, and the size of the cooling system, which covers the outer surface of the battery pack. In connection with this case, the above-mentioned prior arts essentially include an intake duct for introducing air from the outside of the vehicle or the cabin into the battery pack and an exhaust duct for discharging the air having passed through the battery pack, which has been heated, out of the vehicle. These ducts have a predetermined size, and therefore, the ducts serve as a principal factor deciding the size of the battery pack based on the cooling system for the battery module with the same condition.